摘要:

This paper reviews the impact of digital computers on acoustics research since their introduction about a decade ago. The influential rôle that computers have attained in acoustics has resulted from their imaginative use as research tools for analysis, control of experiments, modeling, and simulation—rather than from straightforward calculating applications. Illustrative examples discussed in this paper include modeling of the human speech‐production process and the mechanical and neural aspects of hearing, speech analysis and synthesis, automatic speech and speaker recognition, generation of musical sounds and psychoacoustic test stimuli, study of the perceptual correlates of acoustic stimuli, multidimensional scaling, simulation of ray propagation in the deep ocean and in reverberant enclosures, acoustic measurements in concert halls, digital modeling of auditorium designs. Monte Carlo simulation of wave propagation in multimode transmission media, and acoustic image reconstruction of unknown objects by “inverse diffraction” on the computer.

ISSN:0001-4966    

DOI:10.1121/1.1911577

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The equations of motion of a vibrating string are derive, and it is shown that a coupling exists between the longitudinal and transverse modes of vibration. Free transverse vibration of small order, under sinusoidal initial conditions, is analyzed. Under these conditions, the equations are separable. The time‐dependent parts of the equations are solved by the method of variable amplitude and phase. It is seen that, when the vibration is nonplanar, part of the energy oscillates between the mutually perpendicular transverse components with a frequency proportional to the nonlinearity parameter α. The path of any point on the string is shown to be an ellipse with slowly rotating and shrinking axes.

ISSN:0001-4966    

DOI:10.1121/1.1911578

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

A study of the expression for the response power spectral density of linear systems to random pressures shows that the response problem essentially reduces to evaluating the joint acceptance of the system with the pressure field. A novel method using a coordinate transformation is presented. This method enables one to determine very simply the joint acceptance of a beam that has arbitrary end constraints with a pressure field that has a spatial‐pressure correlation function that is easily described mathematically. The joint acceptance of a simply supported beam with a reverberant acoustic field as a function of mode number and nondimensionalized frequency parameter (beam length/acoustic wavelength) has been computed for the first 16 modes. An engineering approximation for the joint acceptance of a simply supported flat plate with a reverberant acoustic field is obtained from the beam results. The method is also used to determine very simply beam and flat‐plate joint acceptance with a turbulent‐boundary‐layer pressure field and with an acoustic plane wave.

ISSN:0001-4966    

DOI:10.1121/1.1911579

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The Mindlin‐McNiven equations are used to study the response of a linearly elastic semi‐infinite rod to a time‐varying pressure suddenly applied to its otherwise free end. The solution is presented as the sum of two parts. The first part is the response that is obtained if the end to which the pressure is applied is restrained from any radial motion. The second part represents the difference in response that arises due to a relaxation of this radial constraint. A numerical investigation of the latter term in the Fourier transform domain discloses two poles, symmetrically placed with respect to zero frequency, which are close to but immediately below the real frequency axis. These poles are the source of the edge‐resonance phenomenon for steady vibrations that has been reported by McNiven and are also the source of the long tail noted in the experiments of Oliver. The form of the correction term in the real time domain is obtained by the method of steepest descent for times in the vicinity of that at which a saddle point comes closest to colliding with each of these poles in the complex frequency plane.

ISSN:0001-4966    

DOI:10.1121/1.1911580

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The exact solution for the symmetric two impacts/particle/cycle motion of ann‐unit impact damper attached to a sinusoidally excited primary system is derived analytically, and its asymptotically stable regions are determined. Simulated motion on a digital computer and experimental studies with a mechanical model are presented, and they show good agreement with theoretical results. It is found that properly designed multiple‐unit impact dampers are more efficient than equivalent single‐unit impact dampers in regard to vibration reduction and noise level of operating units.

ISSN:0001-4966    

DOI:10.1121/1.1911581

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The use of cross correlation as a tool for analyzing propagation of energy in structural systems is investigated. Each energy‐transmission path will have a characteristic delay time, and examination of the cross‐correlation function of input and response can guide in the determination of the most significant path or paths. Difficulties occur in distributed systems or when the propagation is by a dispersive mechanism. The principles of correlation analysis are examined for both dispersive and nondispersive systems. Experimental evidence is presented that supports the theory and concepts developed. On the basis of these preliminary results, it appears that the technique holds promise and bears further investigation.

ISSN:0001-4966    

DOI:10.1121/1.1911582

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

An integral equation relates the single frequency vertical distribution of ambient ocean noise to the measured array output when the noise power at the array arises from the superposition of uncorrelated plane waves. This integral equation has an infinite number of solutions. However, from the physical viewpoint, there is one solution, referred to as the “principal solution,” which is the most plausible representation of the true noise field. The “principal solution,” is precisely defined, and then classical Hilbert space theory is used to determine this solution from a finite number of array measurements. The number of measurements required depends only on the interelement spacings of the array. In selecting this finite number of steering angles to make the array measurements, any choice that yields independent samples for a certain finite sequence of trigometric functions is sufficient. Not surprisingly, these measurements contain all the information available in the observed distribution, the array output, and an explicit expression is given for the observed distribution. Special array configurations are exhibited for which the “principal solution” is a partial sum in the Fourier expansion of the true noise field.

ISSN:0001-4966    

DOI:10.1121/1.1911583

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

Three types of waves that contribute to the total acoustic diffracted field of an aluminum cylinder in water are isolated by generating each wave to the exclusion of the other two. The “Franz‐type” or “creeping” wave is generated separately on the outside of aluminum cylinders withkavalues ranging from 54 to 1008. The circumferential‐wave speed is found to be 1% less than that of the free waterborne wave, in agreement with the theory for a rigid cylinder. The attenuation of these waves on aluminum cylinders is significantly less than that predicted by the theory for the rigid cylinder. Another circumferential wave, with approximately a 30° incidence and emergence angle, is found to propagate on the inside of the curved boundary. This wave has an attenuation ranging between 0.10 and 0.18 Np/rad and has a speed of 2.5 times that of the free waterborne wave. This is classified as a “Rayleigh type” wave. A third wave is observed that is similar to the wave generated at 30° incidence but has a 15° incidence and emergence angle. The attenuation is between 0.08 and 0.14 Np/rad and has a speed of 6.5 times that of the free waterborne wave. Experimental measurements of differential‐scattering cross section are compared with those calculated by means of the creeping‐wave formulation.

ISSN:0001-4966    

DOI:10.1121/1.1911584

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

Ray geometry, travel time, and spreading loss are studied in a horizontal channel in which sound speed depends on range. Formulas valid for a general sound‐speed function are developed, and then specialized to the class of linear functions. Rays reaching a fixed receiving point are then isolated and studied. Properties of corresponding arrivals at a fixed receiving point are compared for the cases of a range gradient channel and a constant sound speed channel. Differences in initial inclination angle, travel time, and spreading loss are found and bounds on these differences are obtained. For a CW source, the total field at a receiving point is then determined. It is demonstrated that the introduction of even a weak range gradient causes major changes in the amplitude and phase, including the occurrence of interference nulls accompanied by a sharp offset in phase. Finally, approximate formulas are developed for the phase shift of the total field, caused by a constant range gradient, relative to the phase in isospeed channels.

ISSN:0001-4966    

DOI:10.1121/1.1911585

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The attenuation of small perturbations in the shape of a plane shock wave is studied for three distinct cases — (A): when a rigid boundary (wall) parallel to the plane of the unperturbed shock is present; (B): when a perturbed interface between two different media exists in the wake of the shock; (C): when there is no boundary (free space). The solution is obtained by extension of a method due to Zaidel. It is shown that for weak shock waves the attenuation becomes very weakly dependent on the nature of the boundary. Numerical results are obtained for shock waves with initially sinusoidal perturbations and initially Gaussian perturbations. For initially sinusoidal perturbations, Case (A) shows the slowest damping (highest peak‐to‐peak ampli‐after some time) whereas Case (B) exhibits the most rapid damping. On the other hand, an initially Gaussian perturbation shows the slowest damping (magnitude of maximum disturbance) for Case (B) and the fastest damping for Case (A). Furthermore, the Gaussian perturbation damps monatonically with time whereas the sinusoidal perturbation damps approximately in the manner of a zero‐order Bessel function — i.e., in an oscillating fashion.

ISSN:0001-4966    

DOI:10.1121/1.1911586

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP